116,222 reputation
7108215
bio website von-eitzen.de/math/tntrep.xml
location Bonn, Germany
age 48
visits member for 2 years, 2 months
seen 3 hours ago

I did study math and had a knack for it, but I am sooo out of that business now ...


Dec
20
answered Probability of every coin displaying HEAD if a coin is tossed 12 times
Dec
19
awarded  Nice Answer
Dec
19
comment Need help solving a functional equation
Are you sure about the conditions "$x,y>0$ and $x,y\ne 1$"?
Dec
19
comment why function argument is on right side $f(x)$ rather than on left side as $xf$
Some people do use that notation (and they have differnt opinions about $f\circ g$ as well).
Dec
19
answered Homeomorphism vs bijective and continuous
Dec
19
comment Homeomorphism vs bijective and continuous
A homomorphism is usually a nice map between algebraic structures (such as groups). Do you mean homeomorphism (continuous bijection with continuous inverse)?
Dec
19
comment A Fantabulous integer is an integer which has another fantabulous integer smaller than it
You should start "Let $F$ be the set of fantabulous integers. Assume $F$ is nonempty."
Dec
19
comment How can a negative multiplied by a negative give positive?
Maybe you at least agree that $3\times (-2) = -6$. Then note that $(-3)\times (-2)$ should be a number such that $(-3)\times (-2) + 3\times (-2) = \bigl((-3)+3\bigr)\times(-2) = 0\times(-2) = 0$, so it must be $+6$ because only $+6+(-6) = 0$.
Dec
19
comment How to prove that $\mathbb{Q}$ is not the intersection of a countable collection of open sets.
Your first assumption is not correct as $\mathbb R\setminus\mathbb Q$ is a countable intersection of open sets and has no interior point.
Dec
19
revised Polynomial proof qustion
added 27 characters in body
Dec
19
comment What is this group? (Recognising a group from a presentation).
Can you write $b$ in that form?
Dec
19
comment Doubt about Proposition 2.39 in Dana Williams' crossed product book
I cannot access the book page
Dec
19
answered What is this group? (Recognising a group from a presentation).
Dec
19
answered minimal polynomial of roots of irreducible polynomial
Dec
18
reviewed No Action Needed The Monty Hall problem
Dec
18
reviewed Leave Open Calling GAP's StructureDescription from SAGE
Dec
18
comment Congruence system doesn't hold, though it should?
Anyway, $14x\equiv 3\pmod{15}$ immediately gives $x\equiv 12\pmod {15}$ so that we can take a few shortcuts.
Dec
17
answered $\sup \sum a_i \ln(b_i)$ with $\sum a_i = \sum b_i =1$
Dec
17
comment check my short simple proof - Functions are of same magnitude. Asymptotic notation.
Could you elaborate why $\ln((\Theta(f(n)))^2)=\Omega(\ln(f(n)))$?
Dec
16
comment How do I determine $P(E\cap F)$ from $P(F) $ and $P(E \mid F)$?
Youshould know that $P(E\cap F)=P(E\mid F)\cdot P(F)$.